Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, turbine engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants are composed of gaseous compounds, such as the oxides of nitrogen (“NOX”), the oxides of sulfur (“SOx”), CO, CO2, NH3, and soot (particulate matter or “PM”). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amounts of many of these pollutants emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
One method that has been implemented by engine manufacturers to comply with the regulation of engine exhaust pollutants has been to detect the different exhaust pollutants, and then treat the detected constituents through various reduction, conversion, and trapping processes. Many different types of constituent-detecting gas sensors are currently available for this use. Some common examples are semiconductor gas sensors, electrochemical gas sensors, and ionization gas sensors. Typical semiconductor gas sensors operate using a detection mechanism that functions based on a changing conductivity in the presence of a target gas. Although adequate for some situations, semiconductor gas sensors generally require high temperatures to operate (e.g., 200-400° C.), are sensitive to water vapor, become unstable as they age, and lack selectivity. Electrochemical gas sensors operate by oxidizing or reducing the target gas at an electrode, and measuring a resulting current. Electrochemical gas sensors, like semiconductor gas sensors, also require high temperatures (e.g., typically above 326° C.) in order to correctly operate. Finally, typical ionization sensors operate utilizing distinct ionization characteristics that a particular gas possesses. Ionization sensors traditionally require relatively high voltages, consume large amounts of power, and have bulky architectures.
One attempt to improve constituent detection within a gas is described in U.S. Pat. No. 7,529,633 (the '633 patent) issued to Schipper et al. on May 5, 2009. The '633 patent discloses a method of determining the chemical composition of a single- or multi-constituent gas, using a discharge hold-off mechanism. The method of the '633 patent includes creating a voltage between two electrodes, and holding the voltage until breakdown of a first gas constituent is observed. Assuming the gas contains multiple constituents, the method of the '633 patent further includes incrementally increasing the voltage over time until breakdown of a second constituent is observed. The step-changes in the voltage and current over time are then used to identify what constituents are present in the gas. Additionally, the method of the '633 patent includes identifying the concentrations of the detected constituents using a sum of an ion current and an electron current.
There are a number of limitations to the '633 patent's approach that may inhibit commercialization. First, the method of the '633 patent advocates using a constant voltage (i.e., non-pulsed voltage) to identify the gas constituents and their respective concentrations. In a constant voltage system, power consumption will generally be high. Moreover, in a constant voltage system, electrode erosion could become a problem due to the sustained discharge, particularly during a thermal discharge.
The gas monitoring system of the present disclosure addresses one or more of the problems set forth above and/or other problems of the prior art.